The present invention relates to a new and distinct cultivar of Phlox plant, known as Phlox ‘Rocky Road Magenta’ and will be referred to hereafter by its cultivar name, ‘Rocky Road Magenta’, or the “new plant”. The new plant was hybridized by the inventor at a wholesale perennial nursery in Zeeland, Mich. on Mar. 31, 2014 as cross between Phlox subulata ‘Arctic Deep Pink’ (not patented) as the female parent times Phlox douglasii ‘Cracker Jack’ (not patented) as the male parent. The new plant passed initial evaluation on the spring of 2016 and was assigned the breeder code 14-328-1 through the remaining evaluation process. ‘Rocky Road Magenta’ was first asexually propagated by stem cuttings in the greenhouses at the same nursery in Zeeland, Mich. in the summer of 2016. The unique characteristics of the new plant have been found to be reproducible and stable in successive generations of asexually propagated and the resultant plants have been found to be identical to the original selection.